INSECT SPERMATOGENESIS 621 



the tail, as Gatenby shows for P i e r i s b r a s s i c a e . The 

 acrosome behaves at first in a normal manner, so far as can be 

 judged from stages corresponding to that of fig. 55, for it can 

 be readily found in the form of a delicate, elongate rod or 

 thread attached to the nucleus. Gatenby (1917 &) is apparently 

 dealing with an acrosome of this kind in Smerinthus 

 p p u 1 i , as indicated in his fig. 9, which shows a condition very 

 similar to that in Callosamia. As I have shown, the early 

 elongation of the acrosome is in no way dependent on the 

 elongation of the nucleus, and Gatenby's conclusions (pp. 474-5 

 of his paper), from the figure mentioned above, seem to me 

 entirely unwarranted. On the whole, the degeneration pheno- 

 mena in the lepidopteran testis seem still to offer many problems 

 which call particularly for an intensive study of the whole 

 germ-cell cycle for their adequate solution. 



Conclusion. 



As I have indicated elsewhere the primary purpose of this 

 study was to compare the fundamental differences in the sperm 

 formation of Lepidoptera and Hemiptera as brought out by the 

 work of Gatenby and myself. As a result of my observations 

 on the Lepidoptera it appears that such differences as actually 

 occur are primarily ones of detail, and that in all essential 

 respects these two insect groups have a remarkably similar 

 spermiogenesis. Indeed, a further comparison with the 

 Orthoptera and Coleoptera which I have studied gives unmis- 

 takable indication of the fundamental similarity in the pro- 

 cesses of sperm formation in all insects, and discounts in a 

 most decided manner the bizarre accounts of insect spermio- 

 genesis with which the older literature is full. 



This seems to be particularly true of the nebenkern, the 

 history of which I have treated in another paper (Bowen, 

 1922 6). In that paper I made extensive use of Gatenby 's 

 studies of the Lepidoptera because in this group conditions 

 seem unusually favourable for an exact analysis of the early 

 condensation of the nebenkern. I then accepted the account of 

 the mitochondrial ' spireme ', and suggested that the neben- 

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